Amino acid availability is critical for building muscle tissue with or without weight training. The amino acid leucine activates the mTOR pathway and stimulates various intracellular proteins that are vital for building muscle tissue.
A study from Victoria University in Melbourne, Australia found that beginning weight trainers given daily leucine supplements (4 grams per day for 12 weeks) gained more strength than those given a placebo (fake leucine). Supplemented subjects increased 5-rep maximum strength in eight exercises an average of 40.8 percent, while control subjects increased strength by 31 percent.
People often have trouble adjusting to the early phases of weight training. Leucine supplements might help them recover faster and gain more strength. (International Journal Sports Physiology Performance, 6: 39-50)